(1) Field of the Invention
The present invention relates to a graphic display unit which can shift a displayed picture to any desired position by hardware.
(2) Description of the Prior Art
Generally, a graphic display unit comprises a graphic random access memory (RAM) for storing data of a plurality of picture images and a display unit such as a cathode-ray tube (CRT) for displaying, on a display panel, a picture by superimposing the plurality of picture images. In such a graphic display unit, it is often necessary to shift one or more picture images on the display panel to any desired position.
Conventionally, to shift a picture image on the display panel, read addresses of the graphic RAM are changed, by software, by the necessary amount of shift so as to rewrite the picture on the display panel. Due to the use of software, however, there is a problem in that it takes a considerably long time of, for example, several seconds to change the read addresses and to rewrite the picture on the display panel.